Hierarchical Membrane for Photoelectrostatically Gated Monovalent‐Divalent Ion Separation

ABSTRACT Monovalent‐divalent ion separation remains a significant challenge for the selective recovery of ions from aqueous solutions. Here, we report a hierarchical membrane composed of a poly(ionic liquid) photo‐grafted onto a carbon nitride thin film supported on porous anodic aluminum oxide. Under concentration gradient‐driven natural diffusion, the membrane establishes a baseline level of monovalent‐divalent selectivity. However, upon application of light and bias as external stimuli, the hierarchical membrane enables light‐assisted modulation of ion transport, resulting in a significant increase in monovalent‐divalent selectivity by over 200 times for Li + /Mg 2+ and over 500 times for K + /Mg 2+ . Ion selectivity arises from hydration‐dependent mobility and electrostatic confinement within charged nanochannels. This work establishes a simple method to prepare hierarchical membranes for dynamically regulating ion transport and provides design principles for advanced monovalent‐divalent ion separation.